The operating system for IBM's AS/400 midrange line. Introduced in 1988, OS/400 communicates with the hardware through the Licensed Internal Code (LIC) layer, which includes the device drivers. In 2004, OS/400 was renamed i5/OS to coincide with the i5 models of that year. With IBM's rebranding to Power Systems, i5/OS became IBM i. See AS/400, Power Systems and IBM i.